Tommy Sheridan yesterday accused his former close friends and allies of conspiring with MI5 and Rupert Murdoch to "fake" a video which apparently records him confessing to visiting a swingers bar in Manchester. The former Scottish Socialist party leader claimed yesterday that the video was "concocted" by his enemies as part of a concerted effort to smear him and his party which was orchestrated by the News of the World.

Asked why the paper would go to such great lengths to produce a faked tape, he claimed it was in revenge for his libel victory in August. "Why would they want to do this? Because they lost £200,000 in court. They're facing a legal bill of half a million pounds and after the court case Mr Murdoch himself at a meeting said he didn't care how long it takes, he wants that little commie bastard destroyed. That's what's at stake."

His claims came as it emerged that the Crown Office, which oversees prosecutions in Scotland, has launched a criminal inquiry into claims that Mr Sheridan and other witnesses had perjured themselves in his recent £200,000 defamation case against the newspaper.

Extracts from the tape were published last weekend and apparently record Mr Sheridan making several confessions that he made two visits to the swingers bar and had confessed as much at a meeting of the SSP.

The News of the World said the tape - which it said was secretly recorded by Mr Sheridan's best man, George McNeilage, in November 2004 - would be a key part of its appeal against Mr Sheridan's libel victory against the paper in August.

During five weeks of often lurid testimony, 11 former SSP colleagues, including several MSPs, claimed that Mr Sheridan had confessed to his infidelity at a private party meeting in late 2004.

However, the jury found in his favour following emotional denials of the claims by Mr Sheridan and his wife Gayle. The judge awarded Mr Sheridan £200,000 in damages and costs against the NoW, which is contesting the jury's decision.

But the MSP, now leader of the breakaway party Solidarity, insisted yesterday he had never visited Mr McNeilage's home, where the tape was allegedly recorded, and had never made the confessions. "I said it was concocted as soon as I heard about it because I know that I wasn't in the house in question. I have never been in the house in question."

The last time he had spoken with his former friend and best man had been in a car journey through Glasgow that month. It was possible, he claimed, that their conversation then was secretly recorded.

He said some parts of the tape - which were released by the News of the World on Sunday - appeared to be his words "spliced" with other voices. This was "easy" with modern computer technology. "Sometimes you think that maybe sounds like me and then you listen to the tape for a continuous period of six to eight minutes and you can now hear what sounds like water running, you can hear what's in the background and it becomes clear that what's happened is that someone else's voice has been used."

He claimed that Mr McNeilage had been paid £20,000 by the News of the World for the tape, which had been handed to the paper by the SSP soon after the newspaper lost its defamation case.

This, he alleged, marked a new low in the collusion between his political rivals, the SSP, and his political enemies, News International and the intelligence services. It was, he said, the "mother of all stitch-ups".

He added: "I wouldn't be surprised if the state was involved. The state has a fine history of trying to destabilise socialist movements and trade union struggles. They do it for a living. That's why they were set up originally. When the history of this whole episode is written, I think you will find that MI5 certainly was involved."

Even so, he added, he was unable to sue the paper for the latest allegations, saying that he could not afford it since no law firm would take him on a no win, no fee basis after he sacked his last legal team during the libel trial.